Can you identify these fish?
I'll post the answers at the end.
This is a subject that I've been kicking around for opening for discussion for quite some time now. Let's face it, African tiger fish are a pain in the butt to identify. But what is the reason that we have such a hard time identifying the various members of this genus? Why does there seem to be so much variation in vittatus? Well, it's actually pretty simple; there really is just that much variety! I'll try to explain, and I promise to try to keep as much technical jargon out of this as possible.
As of the publication of the writings of Paugy and Guegan in 1989 there have been five recognized species of African tiger fish in Hydrocynus. However, in 2011 an intrepid group of young scientists from the University of Cape Town (Goodier, Cotterill, O’Ryan, Skelton & DeWit) endeavored to perform a complete genetic sampling of the enigmatic members of Hydrocynus.
What they found was interesting indeed. These intrepid scientists found that there were in fact not five genetic populations of African tiger fish as you might expect from the current taxonomic division, but ten! They genetically confirmed the validity of the five species that are currently described on morphological traits. Interestingly though, they discovered five previously unknown genetic heritages!
What are these lineages and how do they fit together?
H. goliath is found in the Congo. They are the most derived species of ATF, having split off from the rest of the taxa approximately 11 million years ago.
An enormous tank raised H. goliath.
H. Brevis is found in the Nile and Gambia rivers where it fills the same ecological niche as H. goliath. In fact, those two species bear a striking resemblance. Brevis is divergent from all species except H. goliath and H. forskahlii about 7.1 million years ago.
H. brevis of various sizes and ages.
H. forskahlii is found in the Nile, Sanaga and Omo rivers as well as in western Cameroon. It diverged from H. brevis about 5.9 mya. Due to how relatively close the divergence of H. brevis and H. forskahlii is to H. goliath when compared to the rest of the taxa, we can deduce that these two are the lineages are the two most closely related to H. goliath. No other species diverged for nearly four million years, which explains why these three lineages are the "bottom lobe" species.
In FATF is where the genetics of the African tiger fishes starts to get a little bit complicated. As I described in my Guide to Identify African Tiger Fish, H. forskahlii actually comprises a species complex, which means that there is more than one distinct genetic population of fish. This species complex is known as the Forskahlii Complex. The two populations of the Forskahlii Complex are H. forskahlii sensu stricto and H. cf. forskahlii population E. The two lineages diverged approximately 2.1 million years ago, with H. forskahlii s.s. Inhabiting all but the western Cameroon portion of the range. H. cf. forskahlii population E is found in the Sanaga rivers and western Cameroon. So, within H. forskahlii, there are two completely distinct populations of fish.
A fine H. forskhalii.
Things get especially convoluted with H. vittatus. In the VATF section of my Guide To Identify African Tiger Fish, I mentioned that there is also a Vittatus Complex. In short, the "Vittatus Complex" is comprised of H. vittatus sensu stricto and three genetically distinct species or subspecies that await scientific description. These are known to science as populations B, C & D of the Vittatus Complex. The Vittatus Complex diverged from the rest of the taxa 3.9 million years ago.
H. vittatus s.s. has the widest distribution of the group. It is found in the Congo, Zambezi and Okavango rivers, coastal river systems south of the Lower Zambezi and in Lake Tanganyika. I want to point out right here that the Zambezi is an eastward flowing river. Remember that for later...
H. cf. vittatus pop. B is found exclusively in Lake Tanganyika.
H. cf. vittatus pop. C is found in the Congo River and the Zambian Congo.
H. cf. vittatus pop. D is found in the Zambian Congo.
Female H. vittatus from the Zambezi River. Zambezi tiger fish are noted for having unusually striking coloration.
"Complex" indeed! As you would expect, there is a great observed variation in what we would consider a "Vittatus Tigerfish". This is supported by the wide variation of genetic lineages within the Vittatus Complex. At the end of the day though, it is unlikely that anyone would mistake any of these fish for anything but a Hydrocynus vittatus. This is why we have come to call anything with stripes VATF; because often enough this is correct. However, the notable exceptions to this rule are the TATF and FATF populations, as explained in the Guide.
H. tanzaniae specimen.
Now how does H. tanzaniae fit into all of this? Things are going to get really interesting here. H. tanzaniae is descended directly from the Vittatus Complex. In complicated terms, H. tanzaniae is a member of the Vittatus Complex that has undergone allopatric speciation to fill an ecological niche equivalent to that which is occupied by H. goliath. What this means is that H. tanzaniae is essentially a VATF trying its best to be a GATF. Interesting.
H. tanzaniae separated from the Vittatus Complex about 1.3 million years ago. It lives in the eastward flowing rivers of Tanzania north of the Zambezi, particularly the Rufiji and Ruasha watersheds. I have noticed a distinct similarity in morphology between Zambezi vittatus populations and H. tanzaniae. The complexity and convolution in Hydrocynus cannot fail to amaze!
H. tanzaniae and a male H. vittatus from the Zambezi. If this image were to be desaturated, they are so similar morphologically that they could easily be mistaken for one anther!
The most enigmatic member of Hydrocynus absolutely has to be Hydrocynus cf. population A. We know nothing about it for sure other than this: It lives in the Congo and it diverged from all of the rest of the taxa as early as 6.9 million years ago. It was sampled and confirmed to exist by Goodier et al., but they did no more research on this fish population than to confirm that it exists. I don't begrudge them this fact however, as their intent wasn't a revision, it was to acquire a genetic profile of the fish in the genus. I would like to propose the hypothesis that this genetic population could be the one which is representative of the almost mythical "Black Goliath". Population A is sympatric with H. goliath. Population A is closest genetically to H. goliath. Population A is highly divergent from the rest of the lineages. The possibilities are tantalizing.
I pray that no other scientists manage to get their hooks into a Black Goliath before I do. I am DYING to examine one. Whether I get funding to go to Africa and catch one or if I manage to import one or some, I don't care. I'd be happy. My goal would be to attempt to verify that either the Black Goliath is morphologically different from H. goliath, that it is the same genetic population as Hydrocynus cf. population A or both, which would allow me to publish a description of the fish. As a nod to Goodier et al.'s "population A" and because I didn't want to choose a species name that started with a letter we already had, I do believe I would call it... "terrible water dog." Hydrocynus atrox.
A Black Goliath from Douglas Dann.
Answers:
H. goliath
H. brevis
H. tanzaniae
H. forskahlii
H. vittatus
I intentionally used less-than-perfect quality pictures for that exercise as those are the type picture we're likely to get in an ID thread.
Reference:
Goodier, S., Cotterill, F., O'Ryan, C., Skelton, P., de Wit, M. (2011). Cryptic Diversity of African Tigerfish (Genus Hydrocynus) Reveals Palaeogeographic Signatures of Linked Neogene Geotectonic Events. Public Library of Science, 6 (12). doi 10.1371.
I'll post the answers at the end.
This is a subject that I've been kicking around for opening for discussion for quite some time now. Let's face it, African tiger fish are a pain in the butt to identify. But what is the reason that we have such a hard time identifying the various members of this genus? Why does there seem to be so much variation in vittatus? Well, it's actually pretty simple; there really is just that much variety! I'll try to explain, and I promise to try to keep as much technical jargon out of this as possible.
As of the publication of the writings of Paugy and Guegan in 1989 there have been five recognized species of African tiger fish in Hydrocynus. However, in 2011 an intrepid group of young scientists from the University of Cape Town (Goodier, Cotterill, O’Ryan, Skelton & DeWit) endeavored to perform a complete genetic sampling of the enigmatic members of Hydrocynus.
What they found was interesting indeed. These intrepid scientists found that there were in fact not five genetic populations of African tiger fish as you might expect from the current taxonomic division, but ten! They genetically confirmed the validity of the five species that are currently described on morphological traits. Interestingly though, they discovered five previously unknown genetic heritages!
What are these lineages and how do they fit together?
H. goliath is found in the Congo. They are the most derived species of ATF, having split off from the rest of the taxa approximately 11 million years ago.
An enormous tank raised H. goliath.
H. Brevis is found in the Nile and Gambia rivers where it fills the same ecological niche as H. goliath. In fact, those two species bear a striking resemblance. Brevis is divergent from all species except H. goliath and H. forskahlii about 7.1 million years ago.
H. brevis of various sizes and ages.
H. forskahlii is found in the Nile, Sanaga and Omo rivers as well as in western Cameroon. It diverged from H. brevis about 5.9 mya. Due to how relatively close the divergence of H. brevis and H. forskahlii is to H. goliath when compared to the rest of the taxa, we can deduce that these two are the lineages are the two most closely related to H. goliath. No other species diverged for nearly four million years, which explains why these three lineages are the "bottom lobe" species.
In FATF is where the genetics of the African tiger fishes starts to get a little bit complicated. As I described in my Guide to Identify African Tiger Fish, H. forskahlii actually comprises a species complex, which means that there is more than one distinct genetic population of fish. This species complex is known as the Forskahlii Complex. The two populations of the Forskahlii Complex are H. forskahlii sensu stricto and H. cf. forskahlii population E. The two lineages diverged approximately 2.1 million years ago, with H. forskahlii s.s. Inhabiting all but the western Cameroon portion of the range. H. cf. forskahlii population E is found in the Sanaga rivers and western Cameroon. So, within H. forskahlii, there are two completely distinct populations of fish.
A fine H. forskhalii.
Things get especially convoluted with H. vittatus. In the VATF section of my Guide To Identify African Tiger Fish, I mentioned that there is also a Vittatus Complex. In short, the "Vittatus Complex" is comprised of H. vittatus sensu stricto and three genetically distinct species or subspecies that await scientific description. These are known to science as populations B, C & D of the Vittatus Complex. The Vittatus Complex diverged from the rest of the taxa 3.9 million years ago.
H. vittatus s.s. has the widest distribution of the group. It is found in the Congo, Zambezi and Okavango rivers, coastal river systems south of the Lower Zambezi and in Lake Tanganyika. I want to point out right here that the Zambezi is an eastward flowing river. Remember that for later...
H. cf. vittatus pop. B is found exclusively in Lake Tanganyika.
H. cf. vittatus pop. C is found in the Congo River and the Zambian Congo.
H. cf. vittatus pop. D is found in the Zambian Congo.
Female H. vittatus from the Zambezi River. Zambezi tiger fish are noted for having unusually striking coloration.
"Complex" indeed! As you would expect, there is a great observed variation in what we would consider a "Vittatus Tigerfish". This is supported by the wide variation of genetic lineages within the Vittatus Complex. At the end of the day though, it is unlikely that anyone would mistake any of these fish for anything but a Hydrocynus vittatus. This is why we have come to call anything with stripes VATF; because often enough this is correct. However, the notable exceptions to this rule are the TATF and FATF populations, as explained in the Guide.
H. tanzaniae specimen.
Now how does H. tanzaniae fit into all of this? Things are going to get really interesting here. H. tanzaniae is descended directly from the Vittatus Complex. In complicated terms, H. tanzaniae is a member of the Vittatus Complex that has undergone allopatric speciation to fill an ecological niche equivalent to that which is occupied by H. goliath. What this means is that H. tanzaniae is essentially a VATF trying its best to be a GATF. Interesting.
H. tanzaniae separated from the Vittatus Complex about 1.3 million years ago. It lives in the eastward flowing rivers of Tanzania north of the Zambezi, particularly the Rufiji and Ruasha watersheds. I have noticed a distinct similarity in morphology between Zambezi vittatus populations and H. tanzaniae. The complexity and convolution in Hydrocynus cannot fail to amaze!
H. tanzaniae and a male H. vittatus from the Zambezi. If this image were to be desaturated, they are so similar morphologically that they could easily be mistaken for one anther!
The most enigmatic member of Hydrocynus absolutely has to be Hydrocynus cf. population A. We know nothing about it for sure other than this: It lives in the Congo and it diverged from all of the rest of the taxa as early as 6.9 million years ago. It was sampled and confirmed to exist by Goodier et al., but they did no more research on this fish population than to confirm that it exists. I don't begrudge them this fact however, as their intent wasn't a revision, it was to acquire a genetic profile of the fish in the genus. I would like to propose the hypothesis that this genetic population could be the one which is representative of the almost mythical "Black Goliath". Population A is sympatric with H. goliath. Population A is closest genetically to H. goliath. Population A is highly divergent from the rest of the lineages. The possibilities are tantalizing.
I pray that no other scientists manage to get their hooks into a Black Goliath before I do. I am DYING to examine one. Whether I get funding to go to Africa and catch one or if I manage to import one or some, I don't care. I'd be happy. My goal would be to attempt to verify that either the Black Goliath is morphologically different from H. goliath, that it is the same genetic population as Hydrocynus cf. population A or both, which would allow me to publish a description of the fish. As a nod to Goodier et al.'s "population A" and because I didn't want to choose a species name that started with a letter we already had, I do believe I would call it... "terrible water dog." Hydrocynus atrox.
A Black Goliath from Douglas Dann.
Answers:
H. goliath
H. brevis
H. tanzaniae
H. forskahlii
H. vittatus
I intentionally used less-than-perfect quality pictures for that exercise as those are the type picture we're likely to get in an ID thread.
Reference:
Goodier, S., Cotterill, F., O'Ryan, C., Skelton, P., de Wit, M. (2011). Cryptic Diversity of African Tigerfish (Genus Hydrocynus) Reveals Palaeogeographic Signatures of Linked Neogene Geotectonic Events. Public Library of Science, 6 (12). doi 10.1371.
